1. Field of the Invention:
This invention relates to a fluid circuit system for operating a bidirectional hydraulic motor adapted, for example, to drive or gyrate the upper vehicle body of an earthmover such as, for example, a power shovel loader etc.
2. Description of the Prior Art:
In Japanese Patent Application Provisional Publication No. 55-142105, there is disclosed a fluid circuit system for operating a bidirectional hydraulic motor, comprising two main conduits located in parallel relationship with each other for supplying the fluid under pressure delivered by a main hydraulic pump through a directional control valve into the bidirectional hydraulic motor; a gyratory brake means of mechanical type for braking the hydraulic motor adapted to be actuated by the resilient force of a spring and also released by the fluid pressure; and a conduit connecting a pressure chamber of said gyratory brake means to an auxiliary pressurized fluid supply source through a changeover or control valve, said control valve being adapted to be held normally at a cut-off position and also changed over, when actuated, to a communicating position by the action of the pressurized fluid supplied through pilot conduits by the main hydraulic pump into said bidirectional hydraulic motor or by the action of the pressurized fluid delivered through pilot conduits by an auxiliary hydraulic pump adapted to be driven by said bidirectional hydraulic motor, the arrangement being made such that when said bidirectional hydraulic motor is driven or rotated said gyratory brake means is released, whilst when rotation of said hydraulic motor is stopped said brake means is rendered operative to effect a brake action.
This hydraulic circuit system is advantageous in that since it is capable of effecting a mechanical brake action when the bidirectional hydraulic motor is stopped the gyratory upper unit can be held at a desired angular position; however, it is disadvantageous in that since, in this fluid circuit, the gyratory brake means is arranged to be released by the action of the pressurized fluid supplied into the hydraulic motor or by the fluid under pressure delivered by the auxiliary hydraulic pump, and is rendered operative to effect a brake action by the resilient force of a spring when the pressure of the pressurized fluid is lowered, the gyratory brake means cannot be actuated to effect a brake action or released at a desired angular position.